An engine of a vehicle may include cylinders having a direct injection fuel injector and a port injection fuel injector. The port injection fuel injector may be supplied with gasoline only from a first fuel storage tank and the direct injection fuel injector may be supplied with ethanol only from a second fuel storage tank. This engine configuration is one example of what may be referred to as an “ethanol boosted system” or EBS. This engine configuration may enhance engine operating efficiency and improve fuel economy performance. For example, under increased torque demand conditions, the port injection fuel injector may inject a reduced amount of gasoline and the direct injection fuel injector may inject ethanol to abate engine knock which otherwise would be caused by the increased torque.
The inventors herein have recognized issues with the above approach. In particular, in the above engine configuration, if the fuel storage tank that supplies ethanol to the direct injection fuel injectors becomes empty, or too low, then little or no fuel is supplied to the direct injection fuel injectors. Over time, the direct injection fuel injectors may become overheated due to a lack of fuel flowing through the direct injection fuel injectors potentially resulting in degradation of the direct injection fuel injectors.
At least some of the above issues may be overcome, in one approach, by a method of controlling fuel supplied to an engine of a vehicle, the vehicle including a first fuel storage tank to store a first type of fuel and a second fuel storage tank to store a second type of fuel, the engine including at least one cylinder having a port injection fuel injector being supplied with fuel from at least one of the first fuel storage tank and the second fuel storage tank and a direct injection fuel injector being selectively supplied with fuel from one of the first fuel storage tank and the second fuel storage tank, the method comprising: at a first condition, supplying at least some of the second type of fuel from the second fuel storage tank to the direct injection fuel injector and supplying at least some of the first type of fuel from the first fuel storage tank to the port injection fuel injector; and at a second condition, supplying at least some of the first type of fuel from the first fuel storage tank to the direct injection fuel injector.
In one example, the first and second conditions may include the amount of fuel in the second fuel storage tank exceeding (or not exceeding) a threshold amount. Thus, at least some of the first type of fuel from the first fuel storage tank may be supplied to the direct injection fuel injectors when there is little or no fuel in the second fuel storage tank. By supplying fuel to the direct injection fuel injectors from a different fuel source when fuel from a first source is not available or too low, overheating of the direct injection fuel injectors may be reduced. In this way, the direct injection fuel injectors of the ethanol boosted system may be made more robust.
Additionally, the delivery of different source fuels to the direct injection fuel injectors may be beneficial during other operating conditions, such as if a fuel tank is mis-fueled, etc.
Furthermore, when little or no ethanol is available and the direct injection fuel injectors are supplied with gasoline, fuel injection may be adjusted so that the direct injection fuel injectors may perform stratified injections of gasoline, under some conditions. By performing stratified injections of gasoline, ultra-lean mixtures of fuel and air may be stably combusted resulting in improved fuel economy relative to combustion of port injected gasoline. In this way, operating efficiency and fuel economy performance gains may be realized under vary operating conditions of the engine.